Transmission/subtransmission mechanism

ABSTRACT

In a transmission of the type which includes a main transmission mechanism equipped with gear trains of a plurality of transmission stages disposed between an input shaft capable of being connected to a crank shaft of an engine and an output shaft parallel to the input shaft and a sub-transmission mechanism transmitting the driving force from the input shaft to a driven gear of the output shaft via gear trains of other transmission stages, and which is supported so as to project from an engine case along the axis of the crank shaft, the improvement wherein an output gear common to said main and sub-transmission mechanisms is disposed at the end of the output shaft on the engine side and the driven gear is disposed on the output shaft in the proximity of the output gear.

BACKGROUND OF THE INVENTION

This invention relates to a transmission which includes a main transmission mechanism equipped with gear trains of a plurality of transmission stages disposed between an input shaft capable of being connected to a crank shaft of an engine and an output shaft parallel to the input shaft and a sub-transmission mechanism transmitting the driving force from the input shaft to a driven gear of the output shaft via gear trains of other transmission stages, and which is supported while projecting from an engine case along the axis of the crank shaft.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a transmission which can limit the rigidity of a transmission case to a relatively low level and can thus reduce the overall weight.

In the transmission in accordance with the present invention, an output gear which is common to both main and sub-transmission mechanisms is disposed at the end of an output shaft on the engine side and a driven gear of the sub-transmission mechanism is disposed on the output shaft at a position close to the output gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and the attendant advantages of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

The accompanying drawings illustrate one embodiment of the present invention, wherein:

FIG. 1 is a schematic view showing the overall driving system in the form of skeleton;

FIG. 2 is a transverse sectional view showing in detail the transmission gear; and

FIG. 3 is a simplified sectional view taken along line III--III of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. Referring initially to FIG. 1, the engine E is shown mounted transversely to the front part of the car body, that is, a crank shaft 1 (see FIG. 2) is disposed in the direction of width of the car body. A transmission means 7 equipped with a clutch 2, a transmission 3, a first differential gear 4, a second differential gear 6 and the like is supported at one side of the engine E that corresponds to the end portion of the crank shaft 1, in such a fashion as to protrude outward in the axial direction of the crank shaft 1. The driving force of the engine E is transmitted to the first differential gear 4 through the clutch 2 and the transmission 3, and from the first differential gear 4 to the second differential gear 6. The driving force from this second differential gear 6 is transmitted to a front wheel 12 on the right through a driving shaft 8, a universal joint 9, a driving shaft 10 and a second universal joint 11 and also to a front wheel 17 on the left through a driving shaft 13, a universal joint 14, a driving shaft 15 and another universal joint 16. The driving force of the engine E is also transmitted to a propeller shaft 19 from the first differential gear 4 through a universal joint 18 and the rotating driving force of this propeller shaft 19 is applied to a third differential gear 21 through a universal joint 20, from thence to a rear wheel 26 on the right through one of the driving shafts 22 connected to the third differential gear 21, a universal joint 23, a driving shaft 24 and a universal joint 25 as well as to a rear wheel 31 on the left through the other driving shaft 27, a universal joint 28, a driving shaft 29 and a universal joint 30. Thus, the engine E drives the front wheels 12, 17 and rear wheels 26, 31 on the right and left.

Referring to FIG. 2 which illustrates in detail the transmission means 7, the clutch 2 is shown in a clutch case 33 which is integral with the engine case 32. The crank shaft 1 is connected to the input shaft 35 of the transmission 3 when the clutch 2 becomes operative due to the inactuation of a release arm 34.

Referring also to FIG. 3, the transmission 3 is shown placed in a transmission case 36 which is integral with the clutch case 33, and is equipped with a main transmission mechanism 37 and a subtransmission mechanism 38. The main transmission mechanism 37 includes the afore-mentioned input shaft 35 having the same axis as that of the crank shaft 1, an output shaft 39 parallel to the input shaft 35 and gear trains 40 through 45 for the first through fifth speeds and for reverse, respectively, that are interposed between the input and output shafts 35, 39. The driving force that is transmitted from the input shaft 35 to the output shaft 39 through the selected gear train of these gear trains 40-45 is outputted from an output gear 46 disposed at the end of the output shaft 39 on the engine side.

The sub-transmission mechanism 38 includes a first idle gear 47 parallel to the input shaft 35, a second idle gear 48 coaxial with the first idle gear 47, a driven gear 49 disposed on the output shaft 39 at a position close to the output gear 46, and a mesh and mesh-release gear 50 common to the second idle gear 48 and the driven gear 49. This mechanism is used for the low speed operation of below the first speed.

The transmission means 7 has a relatively large weight and moreover, is cantilevered to the clutch case 33 which is integral with the engine case 32. In such a cantilever support structure, the major proportion of the weight should be arranged as close as possible to the engine side in order to reduce the rigidity of the transmission case 36 and that of the engine case 32 to which the former is fitted, and thus to reduce the overall weight. Accordingly, if the output gear 46 and the driven gear 49 having relatively large weights are disposed at the position close to the end of the output shaft 39 near the engine E, the sub-transmission mechanism 38 can be disposed close to the engine E. In consequence, the weight distribution of the transmission means 7 can be shifted towards the engine E. It is thus possible to form the transmission case 36 and the engine case 32 as having a relatively thin thickness to reduce the rigidity required by those cases and eventually, to reduce the overall weight of the engine including the transmission means 7.

The output gear 46 meshes with a reduction gear 53 which is rotatable around the driving shaft 8 parallel to the output shaft 39 at the rear of the transmission 3. Both output and reduction gears 46, 53 are helical gears. Planet gears 54 are pivotally supported at four positions in the circumferential direction of the reduction gear 53 and these planet gears 54 mesh with the inner gear 56 of a ring gear 55 and with a sun gear 57, respectively, thereby forming the first differential gear 4. The sun gear 57 is disposed integrally with an inner cylinder 58 encompassing the outer circumference of the driving shaft 8 while the ring gear 55 is disposed integrally with an outer cylinder 59 encompassing the outer circumference of the inner cylinder 58.

The outer gear 60 of the ring gear 55 has a helical shape and meshes with a gear 61 which is also a helical gear. The gear 61 is disposed integrally with a rotary shaft 62 which is parallel to the driving shaft 8. A bevel gear 63 is further disposed integrally with this rotary shaft 62. This bevel gear 63 meshes with another bevel gear 52 which is disposed integrally with a rotary shaft 64 extending in a direction at right angles with respect to the rotary shaft 62. The rotary shaft 64 is connected to the propeller shaft 19 via the universal joint 18. Accordingly, the direction of the driving force from the first differential gear 4 is converted at right angles to the crank shaft 1 via the gear 61 and the bevel gears 63, 52 and the driving force is then transmitted to the propeller shaft 19.

Here, the mesh state between the output gear 46, the reduction gear 53, the outer gear 60 of the ring gear 55 and the gear 61, that are the helical gears, will be explained with reference to FIG. 3. The mesh portion between the outer gear 60 of the ring gear 55 and the gear 61 is closer to the engine E than the axis of the driving shaft 8, so that the center angle α described between the mesh portion 66 of the output gear 46 with the reduction gear 53 and the mesh portion 65 described above can be minimized, preferably below 90°. In other words, since thrust force acts upon the mesh portion of the helical gears, mutually opposing forces will act upon both mesh portions 65, 66 along the axis of the driving shaft 8 if the output gear 46 and the gear 61 are positioned on the opposite sides to each other with respect to the driving shaft 8, whereby bending moment will act upon the driving shaft 8. In such a case, the strength of the driving shaft 8 as well as strength of bearings 67, 68 supporting the driving shaft 8 must be increased. However, since both mesh portions 65, 66 are positioned close to each other as described above, the thrust forces occurring at the mesh portions 65, 66 offset each other and the bending moment acting upon the driving shaft 8 can be reduced. Hence, the strength of the driving shaft 8 and bearings 67, 68 need not be increased. This is advantageous for strength design.

Since the mesh portion 65 is shifted towards the engine E, a sufficient space can be secured at the rear of the transmission means 7, that is, between the transmission means 7 and a dashboard represented by two-dot-chain line as can be seen clearly from FIG. 3. This space can be used for arranging a steering mechanism 70, a leadbeam 71 and the like. Thus, the cabin of the vehicle can also be enlarged.

The second differential gear 6 has the same axis as the first differential gear 4 and is disposed in such a manner as to interpose the clutch case 33 between both differential gears 4, 6. In the second differential 6, the driving shafts 8, 13 are disposed inside the gear box 72 so as to face each other while sharing the same axis. A support shaft 73 crossing at right angles to the driving shafts 8, 13 is fixed to the gear box 72 between both driving shafts 8, 13. The gear box 72 is integrally fixed to the inner cylinder 58 of the first differential gear 4, and bevel gears 74, 75 are fixed to the support shaft 73. The driving shafts 8, 13 penetrate turnably through the gear box 72 and bevel gears 76, 77 meshing with the bevel gears 74, 75 described above are fixed at the end portions of these driving shafts, respectively.

As described above, the first differential gear 4 for driving the front and rear wheel driving systems and the second differential gear 6 for driving the front wheels are disposed on the same axis via the shaft 8. The first differential gear 4 is of the planet gear type with the second differential gear 6 being of the bevel gear type. This makes the overall construction compact. In other words, since the first differential gear 4 is disposed outside the crank shaft 1 of the engine E, its diameter can be made relatively large. Since it is of the planet gear type which occupies a relatively large space in the radial direction, but needs only a limited space in the axial direction, it contributes to the reduction of the width of the transmission means 7 in the axial direction of the crank shaft 1. Due to its arrangement, the second differential gear 6 is disposed at the rear of the engine E and hence, its diameter can not be increased easily. However, its width can be increased and hence, a relatively large width is necessary in the axial direction, but since the differential gear 6 is of the bevel gear type having a relatively small diameter, the amount of projection of the transmission means 7 to the back of the engine E can be reduced. As a result, the transmission means 7 can be made compact as a whole. Moreover, each planet gear 54 of the first differential gear 4 is directly and pivotally supported by the reduction gear 53. The distance between the second differential gear 6 and the reduction gear 53 can be reduced. This also helps reduce the size of the transmission means 7.

The third differential gear 21 (see FIG. 1) is of the bevel gear type having the same construction as the second differential gear 6 and hence, the detailed explanation is hereby omitted.

Next, the operation of this embodiment will be explained briefly. The driving force of the engine E is transmitted from the crank shaft 1 to the input shaft 35 of the transmission 3 through the clutch 2 and then to the output shaft 39 through either the gear train of any of the transmission stages of the main transmission mechanism 37 or the sub-transmission mechanism 38. The driving force from the output shaft 39 is transmitted from the output gear 46 to the reduction gear 53 and then the driving force is divided by the first differential gear 4 to the sun gear 57 and to the ring gear 55. The transmission force transmitted to the sun gear 57 is transmitted to the right and left front wheels 12, 17 through the second differential gear 6. The driving force transmitted to the ring gear 55 is transmitted to the right and left rear wheels 20, 31 through the gear 61, the bevel gears 63, 52, the universal joint 18, the propeller shaft 19 and third differential gear 21.

Incidentally, the sub-transmission mechanism 38 can be constructed for the high speed use of the fifth or higher stages, instead of the low speed use for the first speed or below described above by the provision of appropriate gears.

As described above, in accordance with the present invention, the output gear is disposed at the end of the output shaft on the engine side and the driven gear of the sub-transmission mechanism is disposed at a position close to the output gear. According to this arrangement, the relatively heavy portion of the transmission is shifted towards the engine and it becomes therefore possible to reduce the rigidity necessary for the engine case and the transmission case supported by the former. As a result, the overall weight can be reduced.

It is readily apparent that the above-described transmission meets all of the objects mentioned above and also has the advantage of wide commercial utility. It should be understood that the specific form of the invention hereinabove described is intended to be representative only, as certain modifications within the scope of these teachings will be apparent to those skilled in the art.

Accordingly, reference should be made to the following claims in determining the full scope of the invention. 

What is claimed is:
 1. A transmission/subtransmission mechanism, connected to an engine for transmitting power to a drivetrain, comprising:a two-shaft main transmission having a plurality of gear stages disposed between an input shaft driven by the crankshaft of the engine and an output shaft parallel to said input shaft for transmitting power from said input shaft to said output shaft at predetermined gear ratios, said plurality of gear stages including at least two forward gear stages; a subtransmission for providing forward low speed operation below the lowest of said forward gear stages, said subtransmission being interposed between said input shaft and said output shaft when said subtransmission is engaged, said subtransmission transmitting power from said input shaft to said output shaft at a different ratio from the ratios of the main transmission, and wherein said main transmission and said subtransmission are disposed proximal to an extension of the axis of the engine crankshaft and are housed in a transmission case formed continuously with an engine case; a driven gear on said output shaft directly receiving the transmitted power from said subtransmission; and an output gear common to said main transmission and said subtransmission, for transmiting power from said output shaft to the drivetrain, and said output gear being disposed on said output shaft at an end nearest the engine, said driven gear being disposed proximal to said output gear.
 2. The transmission/subtransmission mechanism of claim 1, wherein said subtransmission comprises two intermediate shafts extending generally parallel with said input and output shafts, and said two shaft main transmission additionally comprises a reverse shaft, such that said intermediate shafts and said reverse shaft are located on radially opposite sides of said input shaft. 